This invention relates generally to septic systems that employ discharge pumps for removing waste water from a waste water storage tank or septic tank, and more particularly to the apparatus and method employed for controlling the pump in response to the level of waste water within the septic tank.
More specifically, the invention relates to liquid transfer systems that require timed control of liquid transfer events, such as a septic tank that delivers effluent to a drain field or other destination in controlled quantities or doses. Such transfer systems typically convey a specific volume of liquid, i.e., one or more doses at timed intervals wherein the number of such doses depend upon the liquid level in a storage tank as measured by a liquid level measuring device. In addition, these systems typically initiate and terminate liquid transfer events when the liquid in the storage tank reaches a predetermined level. Typically, liquid transfer systems used in septic tank applications have been controlled using float switches and mechanical timers. Similarly, pressure switches, ultrasonic sensors, and other devices have been used to measure liquid levels in these types of liquid storage tanks. However, these methods are typically either excessively expensive and/or only provide transfer cycle initiation and termination control at specific liquid levels. Moreover, the liquid level sensing ability of low cost pressure transducers is typically inaccurate due to changes in atmospheric pressure, temperature, humidity, and absorption of air into the liquid layer within or below the pneumatic pressure accumulator.
Accordingly, devices for detecting and controlling the level of liquids in liquid storage tanks are well known and used extensively for controlling the quantity of liquid in waste water storage tanks that employ pumps to remove liquid therefrom. For example U.S. Pat. No. 2,948,661 issued in 1960 disclosing a system that employs two differential pressure transmitters for measuring differential air pressure wherein the complexity of a second pressure transmitter is required due to varying liquid levels. In 1962 U.S. Pat. No. 3,025,924 issued disclosing a light sensitive selenium cell for controlling the liquid level in a liquid storage tank. The accuracy of this device, however, depends to a certain extent on the quality of liquid that is being measured.
In 1964 U.S. Pat. No. 3,130,154 issued disclosing a timer clock that controls the closing of a solenoid valve that opens responsive to suction pressure for controlling the liquid level in a tank. Accordingly, its accuracy is dependent upon the quality of supplied suction air.
In contrast, float devices are commonly employed to measure liquid levels and control pumps in tanks. Examples include U.S. Pat. Nos. 3,563,382 and 3,875,051 issued respectively disclosing a float device provided to control the on/off function of a pump in a sewage tank. Likewise, U.S. Pat. Nos. 3,875,051 issued in 1975, 4,230,578 issued in 1980, 4,563,274 issued in 1986, and 5,859,589 along with 5,900,546 issued in 1999, wherein each employ at least one float assembly or float switch to control liquid levels. Importantly, one problem with float-type switches is that it is common for the switch itself to be immersed in the liquid thereby subjecting the switch to corrosion and to solid matter that may be in the tank.
Other liquid level measuring devices include U.S. Pat. No. 3,957,633 disclosing a sensor comprising either a photometric or electrolytic operated device to detect liquid levels; and U.S. Pat. Nos. 4,715,966 and 5,319,973 which employ an ultrasonic device to detect and control liquid levels. The functioning of these devices, however can be effected by the quality of the liquid being measured or sensed.
Finally, pressure transducers are also employed for liquid level detection and control as disclosed in U.S. Pat. Nos. 4,594,153 which employs a pressure transducer that is in continuous communication with a suction conduit to detect liquid levels; 5,312,594 which employs a level controlling device that requires two pressure transducers in its operation; 5,319,973 which employs a ultrasonic transducer that emits ultrasonic pulses toward a float device to control the level of liquid in a tank; 5,963,883 which employs a pair of differential pressure transducers to measure liquid levels; and U.S. Pat. No. 6,004,463 which comprises a pressure transducer means to sense air pressure. Importantly, one problem with pressure transducers, is that the quality of air or liquid that a pressure transducer is in communication with will often change over extended periods of time.
While most of the above noted level detection devices will respond to liquid levels to control pumps in liquid storage tanks, most are in one way or another inaccurate to begin with, or become inaccurate over time, and in addition are complex or expensive to maintain.
Accordingly, a need remains for an accurate, reliable, inexpensive, and simple device or system to monitor and control the level of liquids in waste water tanks in a way where accuracy is maintained over long periods of time with little or no maintenance being required.
One object of the invention is to accurately control the liquid level in a waste water septic tank.
A second object is to accurately control the amount of liquid dispersed into a septic drain field at predetermined intervals.
Another object is to precisely control the on/off switching of an electrically operated pump in a pneumatic pump control system for sequentially switching on and off an electrically operated pump.
Yet another object is to control the quality of air disposed for communicating changes in pressure thereof responsive to varying liquid levels within a waste water septic tank.
A further object is to precisely monitor and control the pumping activity of an electrically operated pump disposed within a waste water septic tank for pumping waste water into a drain field.
Still another object is to economically control the pumping of waste water from a waste water septic tank.
An additional object is to prevent the degeneration of accuracy of a liquid level measuring device used to control a pump, when the level measuring device is employed over extended periods of time without requiring maintenance.
The invention is a pneumatic pump control system for sequentially switching on and off an electrically operated pump disposed in a liquid storage tank for waste water typically referred to as a septic tank. Typically such tanks are provided for receiving liquids and or a combination of liquids and solids disposed below an upper layer of air. In general, the pneumatic pump control system comprises a pneumatic pressure accumulator that is disposed within the liquid storage tank at a predetermined level. The pneumatic pressure accumulator is a dome-type that defines an interior air chamber for containing air, and a lower opening disposed at an elevation that represents a zero reference level within the tank. Importantly, the lower opening is in communication with the liquids in the liquid storage tank when the level of liquid is as high as the lower opening.
In addition, a pressure transducer is operatively connected to the pneumatic pressure accumulator for communication with the interior air chamber to measure the differential air pressure between the air within the interior air chamber and the upper layer of air within the liquid storage tank. Specifically, the pressure transducer is adapted to generate an electric output signal that varies according to and corresponding to the changing differential air pressure that fluctuates as the liquid level changes.
In this way, a first activation means can respond to the output signal of the pressure transducer such that when the pressure transducer indicates a pressure that corresponds to a liquid level that has risen above a predetermined start-level elevation, within the liquid storage tank, the pump is activated for a period of time to discharge a predetermined quantity of liquid. This predetermined quantity of liquid is referred to as a normal dose. Importantly, one or more normal doses are executed (cycled) to lower the liquid level to a level at or below the start-level.
Following this, as noted above, the pressure transducer indicates a pressure that corresponds to a liquid level that is at or below the start level elevation, wherein a clearing activation means responds by activating the pump for a period of time to discharge a predetermined quantity of liquid that is referred to as a clearing dose. As will be explained in more detail in the description of the preferred embodiment, one or more clearing doses are executed to lower the liquid level to a level below the zero reference level so that the air captured within the pneumatic pressure accumulator is recharged to be of the same consistency as the upper air layer which is the ambient air entrapped within the liquid storage tank.
The foregoing and other objects, features, and advantages of this invention will become more readily apparent from the following detailed description of a preferred embodiment which proceeds with reference to the accompanying drawings, wherein the preferred embodiment of the invention is shown and described, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.